LONDON (AP) — Opponents of the British government’s plan to deport migrants to Rwanda are preparing for an appeals court hearing Monday amid the political backlash following reports that Prince Charles had privately described the policy as “appalling.”

A coalition of groups including immigration rights advocates and public employee unions will ask the Court of Appeal in London to reverse a lower court ruling allowing the first deportation flight to go ahead as scheduled on Tuesday.

Prime Minister Boris Johnson’s Conservative government in April announced plans to send some undocumented migrants to Rwanda, where their claims for asylum in the east African nation would be processed. If successful, those migrants would stay in Rwanda. Britain paid Rwanda 120 million pounds ($158 million) upfront and will make additional payments based on the number of people deported.

The program is aimed at discouraging migrants from risking their lives by crossing the English Channel in small boats after a surge in such journeys over the past two years. But human rights groups say the policy is illegal, inhumane and will only magnify the risks for migrants.

The debate filled Britain’s news media over the weekend after the Times of London reported that an unidentified person had heard Prince Charles express opposition to the policy “several times” in private conversations.

“He said he thinks the government’s whole approach is appalling,” the newspaper quoted the source as saying.

Charles’ office, Clarence House, refused to comment on “anonymous private conversations,” but stressed that the prince remains “politically neutral.”

Charles’s comments are problematic because he is the heir to the throne and the British monarch is supposed to remain above the political fray.

The reported conversations raise concerns about whether Charles can be a neutral monarch after a lifetime of speaking out on issues ranging from ocean plastic to architectural preservation. Charles, 73, has taken on an increasingly central role in recent months as health problems have limited the activities of Queen Elizabeth II, his 96-year-old mother.

The comments set off a firestorm in British newspapers, with the Daily Express warning the Prince of Wales: “Stay out of politics Charles!” The Mail on Sunday said: “We will not back down on Rwanda, Charles.’’

Johnson’s government shows no signs of changing course.

Northern Ireland Secretary Brandon Lewis, who represented the government on Britain’s Sunday morning TV programs, offered a robust defense of the plan, saying the British government wants to upend the business model of people smugglers.

“The reality is this is a policy that is going to deliver — to ensure that modern slavery and these people smugglers know that their criminal methods will be broken down,’’ he told Sky News.

More than 28,500 people entered Britain on small boats last year, up from 1,843 in 2019, according to government statistics. The risk of such crossings was made clear on Nov. 24, when 27 people died after their inflatable boat sank in the waters between Britain and France.

The Home Office, the agency that oversees border enforcement, launched its own defense of the policy on Sunday, posting comments from a Rwandan government spokesperson on social media.

“It’s about protecting and ensuring the wellbeing and development of both migrants and Rwandans in Rwanda,” the Rwandan spokesperson, Yolande Makolo, said.

A High Court judge in London on Friday rejected a request from opponents of the plan to block Britain's Rwanda asylum flights until the court had reached a decision on whether the program is illegal. The decision allows the flights to begin even as the broader legal challenge moves forward.

That ruling has been appealed to the Court of Appeal, which will hear the petition on Monday.

Government lawyer Mathew Gullick said Friday that 37 people were originally scheduled to be aboard Tuesday’s flight, but six had their deportation orders canceled. The government still intends to operate the flight, he said.

The government has not provided details of those selected for deportation, but refugee groups say they include people fleeing Syria and Afghanistan.

Rwanda is already home to tens of thousands of refugees. Competition for land and resources contributed to ethnic and political tensions that culminated in Rwanda’s 1994 genocide, in which more than 800,000 ethnic Tutsi and the moderate Hutu who tried to protect them were killed.

President Paul Kagame’s government has achieved significant economic progress since the genocide, but critics say it has come at the cost of strong political repression.

The United Nations’ refugee agency has opposed Britain’s plans, saying it's an effort to export the country’s legal obligations to provide asylum to those seeking a safe haven.

“People fleeing war, conflict and persecution deserve compassion and empathy,” said Gillian Triggs, UNHCR’s assistant high commissioner for protection. “They should not be traded like commodities and transferred abroad for processing.”

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Danica Kirka, The Associated Press